This invention relates to circuitry that provides a Direct Current (DC) of a constant voltage to a load. More particularly, this invention relates to circuitry that receives either Alternating Current (AC) and DC of varying voltages from a power source and outputs DC of a constant voltage. Still more particularly, this invention relates to a circuit that receives power from an AC or a DC source and provides DC of a constant voltage of a constant voltage to a signal conditioner in meter electronics of a Coriolis flowmeter.
It is a problem that different countries, even in different regions of countries, that electricity may be delivered in different manners and at different voltages. Some countries may provide DC electricity and other may provide AC electricity. The problem becomes exasperated when wiring in different facilities deliver electricity in different manners and voltages.
Manufacturers of electronic components that are shipped throughout the world are constantly looking for ways in which to provide electricity of a constant current and voltage to a load. The ability to provide a constant current and voltage to a load would save substantial development and manufacture time as one power supply would be used for the component.
One device in which this is a particular problem is a Coriolis flowmeter. A Coriolis mass flowmeter measures mass flow and other information of materials flowing through a conduit in the flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. Nos. 4,109,524 of Aug. 29, 1978, 4,491,025 of Jan. 1, 1985, and Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. These flowmeters have one or more conduits of straight or curved configuration. Each conduit configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional or coupled type. Each conduit is driven to oscillate at resonance in one of these natural modes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter, is directed through the conduit or conduits, and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating, material filled system are defined in part by the combined mass of the conduits and the material flowing within the conduits.
When there is no flow through the flowmeter, all points along the conduit oscillate due to an applied driver force with identical phase or small initial fixed phase offset which can be corrected. As material begins to flow, Coriolis forces cause each point along the conduit to have a different phase. The phase on the inlet side of the conduit lags the driver, while the phase on the outlet side of the conduit leads the driver. Pick-off sensors on the conduit(s) produce sinusoidal signals representative of the motion of the conduit(s). Signals output from the pick-off sensors are processed to determine the phase difference between the pick-off sensors. The phase difference between two pick-off sensor signals is proportional to the mass flow rate of material through the conduit(s).
Meter electronics in the Coriolis flowmeter provide a drive signal to a driver as well as processing signals from the pick-off sensors to determine mass flow rates and other properties of a material. Manufacturers of Coriolis flowmeters such as Micro Motion Inc. of Boulder, Colo. USA sell Coriolis flowmeters to users in various countries throughout the world and desire a circuit for providing power to the meter electronics that provides a DC current that has a constant voltage regardless of power source.
The above and other problems are solved and an advance in the art by power supply circuit that outputs a DC of a constant voltage from an input of either AC or DC at any voltage. One advantage of this invention is that only one power supply circuit must be placed in manufactured component no matter where the component is being used. This decreases the development time for a component as well as reducing the manufacturing costs of the component.
In accordance with this invention, a circuit for supplying a DC output of a desired voltage from an input regardless of the power source includes the following components. A rectifier receives an input current and converts an alternating current (AC) input to direct current (DC) or changes a DC input to a desired polarity. A boost converter receives DC current from the rectifier and outputs current having at least a minimal voltage. The DC current received from the rectifier has an unknown voltage and the boost converter simply boosts the voltage to a minimal level if the current does not have that minimal voltage. A second boost convertor called a buck boost convertor receives the DC current having at least the minimal voltage and outputs DC having a desired voltage.
The circuit may also include a transformer that provides a galvanic barrier between the buck booster and a load. The galvanic barrier prevents excess current, voltage, or power from being applied to the load. The circuit may also include an output rectifier that prevents excess current from being applied to the load. An opto-coupled feedback may be connected to the output rectifier. The opto-coupled feedback provides a signal to a buck boost feedback control that regulates current output from the buck-booster converter.
The circuit may also include control circuitry that maintains the at minimal output voltage of current output by the boost converter. The circuit may also include start-up circuitry regulates voltage applied to said control circuitry.